1. Rachel Williams

2. Time travel is a common theme in sci-fi, and can be central to the plot, or merely
a device to set the story in motion. Hard sci-fi examines the causes and effects
of time travel paradoxes, but soft sci-fi usually ignores negative aspects and
focuses on the wonders and adventures. The time travel motif is often seen as a
necessary distancing effect which can allow sci-fi to address contemporary
issues in metaphorical ways, and is valuable in providing a view of history where
every person is significant.
The concept of time travel has always been a popular. It usually involves the
use of some type of advanced technology, like in „The Time Machine‟, „Back to
the Future‟, and „Terminator‟. Movies, such as „Planet of the Apes‟, explain their
depictions of time travel by drawing on physics concepts such as the special
relativity phenomenon of time dilation (travelling near the speed of light) and
wormholes. Some films show time travel being attained from an inner source or
personal power, such as „Donnie Darko‟ and „The Butterfly Effect‟.
More conventional time travel movies use technology to bring the past into the
present, or in a present that lies in our future. The film „Iceman‟ told the story of
the reanimation of a frozen Neanderthal, and the film „Freejack‟ shows time
travel been used to pull victims of horrible deaths forward in time a split-second
before their demise.
One of the most common themes in time travel films is the paradox. In the film
„La jetée‟, the director depicts a person being able to see their future by showing
a child who witnesses the death of his future self. „Back to the Future‟ goes one
step further and explores the result of altering the past, while in „Star Trek‟ the
crew must rescue the Earth from having its past altered by time-travelling
cyborgs and alien races.

3. 1. Change only the fictional characters' histories.
You can't change the history that everybody else has. You can only change the
history of a fiction character. That was how Bob Gale and Robert Zemeckis
got away with it in „Back to the Future‟.
2. Use the alternate-reality loophole.
Science is willing to contemplate the existence of parallel realities, perhaps
an infinite amount. By thinking of „Groundhog Day‟, Ben Ripley, the creator of
„Source Code‟ found his loophole. By creating many alternate realities, the
main character in „Source Code‟ could continually return to the past,
changing anything, but not have to experience the consequences.
3. Inconsistencies be damned.
In „Time After Time‟, Jack the Ripper travels to the future using H.G Wells‟
time machine. One question screenwriter, Nicholas Meyer, wondered was
why Mr. Wells didn‟t just travel back to stop the murderer in the first place?
Meyer‟s says that he would have added something like:“Why don't you wait
for the murderer to show up?” and Mr. Wells responding, “What if I can't stop
him? The guy's carrying around a bunch of knives and he's stronger than me.”
to make it clear how it wouldn‟t be possible to do such a thing.
4. Don't kill your grandfather.
„Back to the Future‟ was a cautionary tale, by Marty fixing one thing, there is
now another problem as a result. In every great time-travel story, you go back
to fix something, but you end up creating something much worse, and you're
just fighting to get back to square one. In „Lost‟, Sayid, is travelling through
the past and encounters young Ben, knowing Ben will one day grow up and
torment the island castaways, Sayid shoots him, but somehow Ben survives.
Damon Lindelof employed the rule „whatever happened, happened‟ and it
Could not be changed. You couldn't go back and kill your grandfather and
create a paradox something will not let that happen.

4. The Hero:
The hero is usually bland and normal and the story revolves around them. This
type of character is meant to be relatable and are normally quite boring. Some
heroes are used to introduce the setting of film, the audience learns as the
character does, asking all the questions the audience would. The hero's job is to
accept the reality of the setting so that we can enter these worlds. An example
is Dr. Will Zimmerman, from „Sanctuary.‟ He is introduced at the start of the first
episode and we learn about the strange world of abnormals as Will stumbles
into a job with a 150 year old caretaker in a gothic Victorian mansion. But there
are different types of heroes. The most important sub-type is the anti hero. In
sci-fi, these heroes have usually fought and lost, or have dubious morals, like
Captain Mal Reynolds, from „Firefly‟. He fought against an oppressive
government, and after losing, he turned to smuggling.
The Geek:
Where would sci-fi be without the geeks, the scientists, and the nerds? They
typically take the form of a scientist or tech support and are usually needed to
deal with some alien technology or some sort of technical problem. A key skill
for every geek is to be able to open the locked door, which reveals adventure,
salvation, or aliens. Some of these scientists have a quirk to them. For example,
Dr. Rodney McKay off „Stargate Atlantis‟ is extremely rude and extremely smart.
In „Sanctuary‟, the main technician is a werewolf, and in „Fringe‟, Walter Bishop
is a genius, but has a piece of his brain missing. The geek is by far the most
iconic sci-fi character. Every sci-fi TV show and movie has a geek, and
sometimes he has the added bonus of being a robot.

5. The Token Alien:
When we're talking sci-fi, aliens are going to come up. There is a natural
progression from space travel to discovering different races. Some are
Primitive and some are hostile and some become regular characters. In
most sci-fi, the token alien is a warrior that could help bring down the bad
guy. Teal'c, from „Stargate SG- 1‟, bald, tall, and imposing, is the perfect
example. He was the right hand man for one of the main villains, but turned
to the human's side when he helped the main characters escape. Another
token alien is Chewbacca from Star Wars; he is the only non-human in the
cast of main characters, other than the dynamic droid duo, C3P0 and R2D2.
The Mentor:
This character is less common in sci-fi than geeks or aliens, but they're still
there, giving sage advice. The mentor has strong morals and gives advice to the
main characters. The most notable mentor in sci-fi is Obi Wan Kenobi from „Star
Wars‟. He guides Luke along his journey to become a Jedi, and when he dies,
another mentor, Yoda, takes over. Dr. Elizabeth Weir of „Stargate Atlantis‟ is a
mentor for an entire crew of adventuring Earthlings. She has a strong moral
compass and often steers the main characters to a moral truth to ensure they do
the right thing.

6. The Opposition:
Every story needs conflict, and sci-fi often gets it from a powerful
enemy who may want to terminate all of humanity. It's common in
science fiction for the villain to be an organization or group of beings
that outnumber the side the main characters are on. It can take the
form of an oppressive government, like The Alliance in „Serenity‟, or
the form of an entire race of aliens, for example the Daleks in „Doctor
Who‟. In sci-fi, the opposition is usually a poorly developed character
with clearly pure evil intentions.
The Expendable Character:
Every sci-fi plot needs one; the guy that dies. These characters are
usually killed off fairly shortly after they have been introduced. They
sometimes die to save other people, usually the main characters, but
that's a death better suited to heroes. The most infamous expendable
characters are the "red shirts" from the original „Star Trek‟ show. If you
didn't know the character's name or they was wearing a red uniform,
they would probably be dead by the end of the episode. Expendable
characters often exhibit a typical human flaw that gets them killed; too
boastful, too curious, too irritable.

7. Even with all these archetypical characters, there are exceptions. A character is often an assorted
bag of different archetypes. The perfect example is The Doctor from „Doctor Who‟. He is the hero,
but he is also an alien with many geeky qualities. The Doctor is also old, and often gives advice to
his companions. Add a little anti-hero and you've got The Doctor. A less complicated example is
Spock, as he's both geek and token alien.
Characters in sci-fi are called upon to make the fantasy world real for viewers. Each contributes a
particular, sometimes peculiar, characteristic that signals to us that we are watching sci-fi and
translates an alien and strange setting into stories we can relate to as humans.

8. Temporal paradox
Also known as „time paradox‟ or „time travel paradox‟ , it is a theoretical paradoxical situation that
happens because of time travel. A time traveller who goes to the past and does something which
prevents him from time travel in the first place, but if he doesn‟t go back in time, he can‟t have done
anything that would prevent him travelling to the past, so time travel would be possible for him. However,
if he goes back in time and does something that would cause him to not make a time machine, he would
not have travelled back in the first place, which causes him to make one, then go back, and not make one.
A typical example of this kind is where a person goes back in time to kill his grandfather before he had
children. If they succeed, one of their parents would never have existed and then they themselves would
never have existed, making it impossible for them to go back in the first place. As well as making them
unable to kill their grandfather, who would continue to produce offspring and restart the situation.
Ontological paradox
The „ontological paradox‟ is a paradox in which information or objects can exist without having been
created. After information or an object is sent back in time, it is recovered in the present and becomes
the very object or information that was initially brought back in time. Numerous sci-fi stories are based
on this paradox, but it has also been the subject of some serious physics articles. Because of the
possibility of influencing the past while time travelling, one way of explaining why history does not
change is to say that these changes already contain self-consistently in the past. A time traveller
attempting to alter the past in this model, would only be fulfilling their role in creating history.
The Novikov self-consistency principle proposes that contradictory consistent loops can form. However,
a scenario can occur where something is passed from the future to the past, which then becomes the
same thing that is subsequently passed back. This not only creates a loop, but a situation where these
items have no clear origin. Physical items are more of a problem than information, because they should
age and increase in entropy according to the Second law of thermodynamics. But if they age at any point
in each cycle, they cannot be the same item to be sent back in time. This creates a contradiction. Another
problem is the „reverse grandfather paradox‟, where whatever is sent to the past allows the time travel in
the first place, such as saving your past self's life, or sending information about the time travel
mechanism. The paradox raises the questions of where, when and by whom the items were created or the
information derived. The bootstrap paradox is similar to, but distinct from, the „predestination paradox‟,
in which individuals or information travel back in time and ultimately trigger events they already
experienced. In the latter case, nothing 'appears out of thin air'.

9. The Paradox
Grandfather Paradox
The „grandfather paradox‟ is where a time traveller goes back in time to before his grandfather married.
Then, the time traveller kills his grandfather, so the time traveller is never born. If he is never born, then
he is unable to kill his grandfather, which means he would be born, and so on. Despite the name, this
paradox doesn‟t just mean preventing your own birth. It applies to any action that makes it impossible to
travel in the first place. The paradox's namesake is merely the most commonly thought of. Another
example would be using scientific knowledge to invent a time machine, then going back in time and
preventing the scientist from discovering the very information that you used to invent the time machine.
The grandfather paradox that disrupts the link between a time traveller‟s present and future may be
regarded as impossible. But, a number of hypotheses describe how to avoid the paradox, such as the
idea that the past is unchangeable, so the grandfather must have already survived the attempted killing,
or the time traveller creates, or joins, an alternate timeline or parallel universe in which the traveller was
never born. A variant of the grandfather paradox is the „Hitler paradox‟, which is a fairly frequent trope in
sci-fi. The protagonist travels back in time to murder Adolf Hitler before he can start World War II. In this
side, rather than physically preventing time travel, the action removes the reason, along with any
knowledge that it ever existed. Because of this, any point in travelling in the first place is erased.
Additionally, the consequences of Hitler's existence are so monumental and all-encompassing that it is
likely that the grandfather paradox would apply in some way. For example, your great-grandparents may
have been Holocaust refugees, or the train your parents met on was constructed as part of the war effort.
Predestination paradox
This can also be called a „causal loop‟ or a „causality loop‟, and is a fairly conventional paradox in
sci-fi. It exists when a time traveller is caught in a loop of events that predestines or predates them to
travel back in time. One way of explaining why history does not change is by saying that whatever
happened must happen. Time travellers attempting to alter the past in this model would only be fulfilling
their role in creating history as it has always been, not changing it. Or the time-travellers' personal
knowledge of history already includes their future travels to their own experience of the past. Time
travellers are in the past, which requires that they were always there. Therefore, their presence is vital to
the future, and they do something that causes the future to happen in the same way that they know has
already happened. It is very closely related to the „ontological paradox‟ and usually occurs at the same
time.